1. Field of the Invention
The present invention relates generally to hydraulic circuit elements which are designed to permit fluid flow when the pressure in an enclosure or downstream of a pump exceeds a predetermined level. The permitted flow of fluid may be directed towards a reservoir or to a point upstream of the supply. Such elements are called safety valves when they act to protect an enclosure, and pressure relief valves when they act to protect a circuit.
2. Description of the Prior Art
Pressure sensitive protective devices for hydraulic circuit elements have hitherto been designed in the form of mechanical devices. The simplest, for example ball-valves, are the least reliable. At high pressures, ball valves are generally the source of dangerous vibration and have to be equipped with hydraulic dampers, which of course increases the cost of the valves undesirably.
Such mechanical devices also suffer from the drawback that they exhibit appreciable variations in their flow pressures.
To reduce pressure variation as a function of flow, pressure-relief valves of the piston spool type have been designed. For high flow rates relief valves using pilot valves have also been designed. However, such valves are expensive and suffer from spring wear or wear on the part of gaiters surrounding their springs.
The prior art protective elements briefly discussed above are convenient enough when used in circuits involving the transfer of water or non-corrosive liquids. However, this is not the case in the chemical industry where corrosive materials may be handled. Even more expensive solutions to the protection problem have had to be resorted to by reason of the mandatory use of special corrosion-resistant metals and in certain cases, precious metals.
Hydraulic pressure limiters are known which operate using elastic obturator devices, and in which the obturator elements themselves furnish the elastic reaction. Such obturator elements have not found significant favour in industry since they are either too thick and insufficiently sensitive, or are too thin and unreliable.